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SubjectRe: [PATCH 1/4] KVM: arm64: Allow saving vgic3 LPI pending status in no running vcpu context
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Hi Marc,

On 1/20/23 2:47 AM, Marc Zyngier wrote:
> On Thu, 19 Jan 2023 01:11:44 +0000,
> Gavin Shan <gshan@redhat.com> wrote:
>>
>> I will have vgic_write_guest_lock() in v2. Note that those 3 paths can't be
>> running in parallel since one switch is shared by them. Alternatively, we
>> extend struct vgic_dist::save_tables_in_progress from 'bool' to 'unsigned long'.
>> Several bit is defined for each site as below. In this way, the 3 paths can be
>> running in parallel:
>>
>> unsigned long struct vgic_dist::save_tables_in_progress
>>
>> #define VGIC_DIST_SAVE_ITS_ITE 0 /* ITS Translation Entry */
>> #define VGIC_DIST_SAVE_ITS_DTE 1 /* ITS Device Table Entry */
>> #define VGIC_DIST_SAVE_ITS_CTE 2 /* ITS Collection Table Entry */
>> #define VGIC_DIST_SAVE_ITS_CT 3 /* ITS Collection Table */
>> #define VGIC_DIST_SAVE_VGIC3_LPI 4 /* VGIC3 LPI Pending Status */
>> #define VGIC_DIST_SAVE_VGIC3_PENDING_TABLE 5 /* VGIC3 Pending Table */
>>
>> The drawback is the calls are limited to 64. If those 3 paths can't be running
>> in parallel, we needn't the extension at all.
>
> It should all be completely sequential. KVM_DEV_ARM_ITS_SAVE_TABLES
> runs in a context where everything is locked, and so is
> VGIC_DIST_SAVE_VGIC3_PENDING_TABLE.
>

Thanks for your confirm. Yeah, it's sequential because 'kvm->lock' is
hold on KVM_DEV_ARM_ITS_SAVE_TABLES and VGIC_DIST_SAVE_VGIC3_PENDING_TABLE.
So all good to have one shared switch. v2 will be posted pretty soon.

Thanks,
Gavin

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